1. Field of the Invention PA1 2. Description of the Prior Art
The present invention relates-to improvements in rotary offset printing presses for producing recto work by means of several offset units with a common impression cylinder. More particularly, the invention relates to sheet-fed multi-color printing presses of the type described which utilize segmented plate and blanket cylinders with a segmented common impression cylinder.
Prior art printing machines, whether designed for offset printing or direct printing, have been utilized for multi-color printing for many years. Two of the most common difficulties with such machines have been (1) the necessity of multiplying the number of plate and blanket cylinders, along with their associated inking rolls, depending on the number of colors to be printed and (2) the necessity in some systems of depositing multiple, colored inks simultaneously on either the plate or blanket cylinders.
The increase in number of printing cylinders and inking roll systems, of course, greatly increases the size and complexity of the printing press and hence the expense of manufacture and operation. In recent years increased emphasis has been placed on reducing the "foot print" of industrial processing equipment including printing presses of all types.
The problems encountered with depositing multiple colors or "sharing" on a single plate or blanket cylinder surface are well known and involve primarily the tendency of the ink to run or blur so as to lose the definition between colors. Additional problems arise when multiple impression cylinders are utilized or when it otherwise becomes necessary to transfer a sheet to be printed from one gripping mechanism to another. The ability to obtain exact registry becomes increasingly difficult with each gripping action.
The U.S. Pat. No. 1,085,224 to Roesen illustrates an example of an offset printing system wherein multiple blanket cylinders B and multiple plate cylinders C, with their associated dampening and inking mechanisms, are arranged about the periphery of a segmented impression cylinder A. In this arrangement, each plate cylinder C transfers only a single color. The result is a rather complex and expensive printing press. British Patent No. 259157 to Vogtlandische Maschinen Fabrik and the German Patent No. 402059 to Vogtlandische Maschinenfabrik are further examples of complex multi-color printing presses wherein each offset plate and blanket cylinder combination transfers only a single color.
The U.S. Reissue Pat. No. 15286 to Schultz et al and U.S. Pat. No. 684,450 to Mowbray both illustrate examples of multi-color printing presses wherein several different colored inks are applied to a single blanket prior to being transferred to the paper to be printed. In the Schultz et al. patent, for instance, each of the three plate cylinders 1 bears a different color design and all three colors are deposited onto each blanket 9-11 of the cylinder 8 prior to printing onto the paper carried by impression cylinder 15. In the Mowbray patent, a form g or a form-cylinder G receives multi-colored designs from color plates prior to transfer from the form to an impression surface carrying the paper to be printed. This type of multi-color printing often results in color-mingling and defamation of design when moist inks are superimposed.